1. Field of the Invention
The present invention relates to a zero insertion force (ZIF) socket for electrically connecting an electronic package such as a ball grid array (BGA) chip with a circuit substrate such as a printed circuit board (PCB), and particularly to a ZIF socket having a uniformly flat cover.
2. Description of the Prior Art
Electrical sockets are widely used in the connector industry for electrically connecting central processing units (CPUs) to printed circuit boards (PCBs) in personal computers (PCs). This is detailed in xe2x80x9cDevelopment of ZIF BGA SOCKETxe2x80x9d (Connector Specifier, February 2002, pp. 18-20), and in U.S. Pat. Nos. 5,722,848 and 5,855,489. Referring to FIG. 4, the electrical socket 6 is designed for electrically interconnecting a CPU (not shown) with a PCB (not shown). The electrical socket 6 mainly comprises a dielectric base 60 having a multiplicity of terminals 63 received therein, a cover 61 slidably mounted on the base 60, and an actuation device 62 engaged with the base 60 and the cover 61. The CPU is attached and seated on the cover 61, with the pins of the CPU extending through the cover 61. By turning the actuation device 62, the cover 61 moves along the base 60 between an open position and a closed position. The CPU and the PCB are electrically connected in the closed position, and disconnected in the open position. The base 60 comprises a widened front portion 600 adjoining a main portion 601. The main portion 601 defines a multiplicity of terminal passageways 6010 in a generally rectangular array, the passageways 6010 interferentially receiving corresponding terminals 63. The cover 61 comprises a raised portion 610 at an end thereof, corresponding to the front portion 600 of the base 60. A multiplicity of holes 611 is defined in the cover 61, corresponding to the passageways 6010 of the base 60.
The cover 61 is integrally formed by injection molding. Forming the cover 61 to have the raised portion 610 is problematic. When flowing molten raw material is injected into a mold from a gate of the mold to form the cover 61, the flowing molten raw material is fed from a material source to a cavity in the mold through a runner system. Because the raised portion 610 is thicker than a main portion of the cover 61, the raised portion 610 of the cover 61 cools at a different rate from that of the main portion. Fibers gradually formed inside the material of the raised portion 610 and inside the material the main portion are arranged differently. This results in different and undesired internal stresses in these portions of the cover 61. These stresses usually cause the main portion and the raised portion to become deformed or deflected. The main portion of the cover 61 is not uniformly flat, and engagement between the base 10 and the cover 11 is incomplete and unreliable. Accordingly, mechanical and electrical connection between the CPU and the socket 6 may be impaired.
Therefore, a new electrical socket which overcomes the above-mentioned problems is desired.
An object of the present invention is to provide a ZIF socket having a cover configured to minimize the risk of distortion of the cover during molding thereof.
Another object of the present invention is to provide a ZIF socket having an inexpensive cover.
To achieve the above objects, a ZIF socket of the present invention is for electrically connecting a central processing unit (CPU) with a printed circuit board (PCB). The socket includes a dielectric base, a cover slidably mounted on the base, an actuator rotatably mounted between the base and the cover, and a multiplicity of terminals received in the base for electrically connecting pins of the CPU with the PCB. The cover comprises a main supporting portion, and a raised portion formed at one side of the supporting portion. The cover defines a multiplicity of holes therein, for receiving the pins of the CPU therethrough. A plurality of blind cavities is defined in a face of the cover that abuts the base. A cross section of each blind cavity is round.
The cover is formed as a single piece by molding. During cooling down of the duly molded cover, fibers gradually formed inside a material of the cover can be arranged randomly relative to a lengthwise axis of the cover. In addition, the material of the cover can be cooled down quickly without producing undesired stress inside the cover. This reduces the risk of deformation of the supporting portion of the cover. Tests have shown that the blind cavities can reduce deformation of the cover by up to 0.1 mm, thus significantly enhancing uniform flatness of the cover. This helps ensure that engagement between the base and the cover is accurate and reliable.